Ruger Mini 14 gas block stamped with a "k" proof mark

As per the web, "K" typically denotes a stainless steel component or is associated with specialized government/law enforcement AC556K / GB military-style configurations.Key Details on Mini-14 "K" Stamped Gas BlocksStainless Designation: In Ruger’s factory coding conventions, the letter "K" used as a prefix or stamp generally indicates a stainless steel finish rather than blued carbon steel.GB and AC556K Context: Factory "GB" (Government Barrel/Bayonet) and selective-fire AC556/AC556K variants featured dedicated gas blocks with integrated bayonet lugs and side-mounted or bottom sling swivels. Genuine original AC556K components are exceptionally rare and valuable on the surplus market.

This item was in a parts bundle that I do not know the history of.